I will attempt to explain what the default files are. If I get these wrong please correct me.

So below is a screenshot of the default files that get placed in your project when you create a navigation based application.

1. CoreGraphics.framework / Foundation.framework / UIKit.framework – These files are created by Apple that contain all the framework code we will be using to create the applications. You will never have to touch these but they should always be in your application.
2. *.xib – These are files used by Interface Builder. I am not sure what they contain. If you double click them, Interface Builder will start
3. *.h – These are header files. They are pretty much the same as all header files like c/c++
4. *.m – These are the meat of the application. They are like .c or .cpp files
5. *.app – This is the application file that will go on the Iphone.